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Common sewage treatment process of aoo



Source: sewage disposal Author: Sewage treatment equipment Date: 2020-02-21 16:05 Browse:

Ao is the abbreviation of anoxic oxygen. Ao process is also called anaerobic aerobic process. A (anaerobic) is the anaerobic section, which is used for nitrogen and phosphorus removal; O (oxic) is the aerobic section, which is used to remove organic matters in water. Its advantage is that in addition to the degradation of organic pollutants, it also has a certain function of nitrogen and phosphorus removal. It uses anaerobic hydrolysis technology as pretreatment of activated sludge, so Ao process is an improved activated sludge process.  

Background knowledge of sewage treatment

common Aoo wastewater treatment Process introduction:

(1) according to the technical policy of urban sewage treatment and pollution prevention, the conventional activated sludge process is generally adopted for the sewage treatment facilities with a daily treatment capacity of more than 200000 cubic meters (excluding 200000 cubic meters / day). Other mature technologies can also be adopted; conventional activated sludge process, oxidation ditch process, SBR process and AB process can be selected for sewage treatment facilities with daily treatment capacity of 100000-200000 cubic meters; For wastewater treatment facilities with daily treatment capacity below 100000 cubic meters, oxidation ditch method, SBR process, hydrolysis aerobic method, AB process and biological filter process can be selected, and conventional activated sludge process can also be selected.

(2) according to the technical policy requirements of urban sewage treatment and pollution prevention and control, the two-stage enhanced treatment process with strong phosphorus and nitrogen removal function should be adopted in areas with control requirements for nitrogen and phosphorus pollutants. A / O process and a / A / O process are generally used for sewage treatment facilities with a daily treatment capacity of more than 100000 cubic meters. In addition to a / O process and a / A / O process, oxidation ditch method, SBR process, hydrolysis aerobic process and biological filter process with phosphorus and nitrogen removal effect can also be selected for wastewater treatment facilities with daily treatment capacity of less than 100000 cubic meters.

(3) according to the technical policy permission of urban sewage treatment and pollution prevention, under the condition of strict environmental impact assessment and meeting the requirements of relevant national standards and water body self purification capacity, the disposal method of urban sewage discharged into large rivers or deep sea can be adopted prudently. When the effluent from secondary treatment of urban sewage can not meet the requirements of water environment, wasteland and idle land can be used in the areas where conditions permit, and natural purification technologies such as land treatment system and stabilization pond can be used for further treatment.

Basic principles

  

 Aoo process flow

 

In Ao process, the front anoxic section and the back aerobic section are connected in series. The do of a section is no more than 0.2mg/l, and the do of O section is 2 ~ 4mg / L. In anoxic stage, heterotrophic bacteria hydrolyze starch, fiber, carbohydrate and other suspended pollutants and soluble organic matter in wastewater into organic acids, which decomposes macromolecular organic matter into small molecular organic matter, and insoluble organic matter into soluble organic matter. When these products are sent into aerobic tank for aerobic treatment, the biodegradability and oxygen efficiency of wastewater can be improved; In anoxic stage, heterotrophic bacteria ammoniate protein, fat and other pollutants (n in organic chain or amino acids in amino acids) to free ammonia (NH3, NH4 +). Under sufficient oxygen supply, nitrification of autotrophic bacteria oxidizes NH3-N (NH4 +) to NO3 -, and returns to pool a through reflux control. Under anoxic condition, denitrification of heterotrophic bacteria reduces NO3 - to molecular nitrogen (N2) to complete C, N, O In the ecological cycle, realize the harmless treatment of sewage.  

 Aoo process equipment

According to the above description of the basic process of biological nitrogen removal, combined with years of coking wastewater denitrification experience, we concluded that (A / O) biological nitrogen removal process has the following advantages:

(1) high efficiency. The process has high removal effect on organic matter and ammonia nitrogen in wastewater. When the total residence time is more than 54H, the COD value of effluent after biological denitrification is reduced to less than 100mg / L after coagulation and sedimentation. Other indexes also meet the discharge standard, and the total nitrogen removal rate is more than 70%.

(2) simple process, low investment and low operation cost. In this process, organic matter in wastewater is used as carbon source for denitrification, so there is no need to add expensive carbon source such as methanol. In particular, in the evaporation of ammonia

When the tower is equipped with a fixed ammonia removal device, the C / N ratio is increased, and the alkalinity generated in the denitrification process correspondingly reduces the alkali consumption required in the nitrification process. (3) Anoxic denitrification process has high degradation efficiency for pollutants. The removal rates of COD, COD and COD in the denitrification process are 36%, 36% and 59%, respectively.

(4) high volume load. Due to the adoption of enhanced biochemistry in nitrification stage and membrane technology of high concentration sludge in denitrification stage, the concentration of nitrification and denitrification sludge is effectively increased, which has higher volume load compared with similar foreign processes.

(5) the anoxic / aerobic process has strong load shock resistance. When the influent water quality fluctuates greatly or the pollutant concentration is high, the process can maintain normal operation, so the operation management is also very simple. Through the comparison of the above processes, it is not difficult to see that the biological nitrogen removal process itself is denitrification, but also degradation of phenol, cyanide, COD and other organic matter. Combined with the characteristics of water quantity and water quality, we recommend anoxic / aerobic (A / O) biological denitrification (internal circulation) process, so that the sewage treatment plant can not only meet the requirements of nitrogen removal, but also meet the discharge standards.
 

Process defects:

1) because there is no independent sludge return system, the sludge with unique function can not be cultivated, and the degradation rate of refractory substances is low;

(2) in order to improve the nitrogen removal efficiency, the internal circulation ratio must be increased, thus increasing the operation cost. In addition, the internal circulation liquid comes from the aeration tank and contains certain do, which makes it difficult to maintain the ideal anoxic state in Section A, which affects the denitrification effect, and the denitrification rate is difficult to reach 90%.

(3) hydraulic retention time (HRT) (nitrification > 6h, denitrification < 2H), MLSS (> 3000mg / L), sludge age (> 30d), N / MLSS loading rate (< 0.03) and total nitrogen concentration in influent (< 30mg / L).

technological process:

After the sewage is collected by the drainage system, it enters into the grid well of the sewage treatment station. After removing the particles and impurities, it enters the regulating tank for homogenization. The pre aeration system is set in the regulating tank, and then the signal is transmitted by the liquid level controller, and then it is sent to the primary sedimentation tank by the lifting pump for sedimentation, The wastewater flows to A-level biological contact oxidation tank for acidification hydrolysis and nitrification and denitrification to reduce the concentration of organic matter and remove part of ammonia nitrogen. Then it flows into the O-level biological contact oxidation tank for aerobic biochemical reaction. Most of the organic pollutants are degraded by biological oxidation and adsorption. The effluent flows to the secondary sedimentation tank for solid-liquid separation, and the supernatant of the sedimentation tank flows into the disinfection tank After contact and dissolution by adding chlorine tablets, the harmful bacteria in the water were killed and discharged to the standard. The debris intercepted by the grid is regularly loaded into the trolley and dumped to the garbage dump. Part of the sludge in the secondary sedimentation tank is returned to the A-level biological treatment tank, and the other part of the sludge is transported to the sludge tank for sludge digestion, and the supernatant of the sludge pool is returned to the regulating tank for further treatment.

   Aoo process facilities

Process facilities

(1) setting purpose of grid well: before domestic sewage enters the regulating tank, a grid is set to remove soft winding materials, large solid particles and floating objects in domestic sewage, so as to protect the service life of follow-up working water pump and reduce the working load of system treatment. Setting features: reinforced concrete structure is set in the grid well, and manual mechanical frame type is adopted for the grille.

(2) the purpose of setting the regulating tank is as follows: After being treated by grid, the domestic sewage enters the regulating pool for regulating and homogenizing the water quantity and water quality, so as to ensure the balance and stability of water quantity and water quality of the subsequent biochemical treatment system. The pre aeration system is set up for aeration and mixing, so as to prevent the suspended particles in the sewage from depositing and stinking, and also play a certain degradation effect on the organic matters in the sewage, so as to improve the impact resistance and treatment efficiency of the whole system Fruit. Setting features: the regulating tank is designed as reinforced concrete structure.

After upgrading to the level 3, the sewage pump is set in the equalization tank. Design features: there are two submersible sewage pumps, the liquid level is controlled, and the pump is a non blocking tear debris pump.

(4) setting purpose of sedimentation tank: solid liquid separation is carried out to remove the peeling off biofilm and suspended sludge in the biochemical tank, so as to truly purify the sewage. Design features: the vertical flow sedimentation tank has good sludge degradation effect. The triangular weir is used to make the water output stable. The sludge is removed to A-level sludge tank by the biological denitrification process, and the sludge is also removed by the biological denitrification process. The tank is designed as A3 steel structure.

(5) purpose of A-level biological treatment tank (anoxic tank) The wastewater is further mixed, and the highly efficient bio elastic filler in the pool is fully used as the bacterial carrier. The refractory organic matter in the sewage is converted into the soluble organic matter by facultative microorganism, and the macromolecular organic matter is hydrolyzed into small molecular organic matter, which is conducive to further oxidation and decomposition of the later O-level biological treatment tank. Meanwhile, under the action of nitrifying bacteria, the returned nitrate carbon nitrogen can be further oxidized and decomposed Nitrification and denitrification, removal of ammonia nitrogen. Design features: built in high-efficiency bio elastic filler, with hydrolysis acidification function, and can be adjusted into o-grade biological oxidation tank to increase biochemical residence time and improve treatment efficiency. The tank is designed as A3 steel structure.

(6) setting purpose of grade O biological treatment tank (biological contact oxidation tank) The tank is the core part of the sewage treatment, which is divided into two sections. In the first section, under the high organic load, through the biochemical degradation and adsorption of a large number of different species of microbial communities attached to the filler, all kinds of organic substances in the sewage are removed, and the organic matter content in the sewage is greatly reduced. In the later stage, under the condition of low organic load, through the action of nitrifying bacteria, ammonia nitrogen in the sewage can be degraded under the condition of sufficient oxygen content, meanwhile, the COD value in the sewage can be reduced to a lower level, so that the sewage can be purified. Design features: the tank is composed of tank body, filler, water distribution device and aeration system. The biofilm process is the main method in this tank, and it has the characteristics of activated sludge process. The packing material in the tank adopts elastic three-dimensional composite packing, which has large specific surface area, long service life, easy to form film, corrosion resistance, and not agglomerate and block. The packing can be freely stretched in the water, and the bubbles in the water can be cut at different levels, which can relatively increase the aeration effect. The packing can be installed in a cage, which is convenient for disassembly and maintenance. At the same time, the design of the two-stage flow diversion tank is more reasonable, which makes the water quality more reasonable. The aeration pipeline in the tank adopts high-quality ABS pipe, which is corrosion-resistant. No clogging, high oxygen utilization. The tank is designed as A3 steel structure.

(7) setting purpose of sedimentation tank: solid liquid separation is carried out to remove the peeling off biofilm and suspended sludge in the biochemical tank, so as to truly purify the sewage. Design features: the vertical flow sedimentation tank has good sludge degradation effect. The triangular weir is used to make the water output stable. The sludge is regularly discharged to the sludge tank by the gas stripping method, and the sludge stripping reflux device is set up. Part of the sludge is returned to A-level biological treatment tank for nitrification and denitrification, which also reduces the generation of sludge and is conducive to the removal of ammonia nitrogen in the sewage. The tank is designed as A3 steel structure.

(8) setting purpose of disinfection tank: the effluent from secondary sedimentation tank flows into the disinfection tank for disinfection, so as to make the effluent quality meet the requirements of sanitary index and discharge out. Design features: disinfection device and guide plate are designed in the disinfection tank, and the disinfection design is to put chlorine into contact with the disinfection method. The utility model has the advantages of convenient and safe discharge into the nearby water area after adding the municipal sewage. The tank is designed as A3 steel structure.

(9) purpose of sludge tank setting: the sludge discharged from the secondary sedimentation tank is regularly discharged into the sludge tank for sludge thickening and aerobic digestion, the sludge supernatant is discharged into the regulating tank for reprocessing, and the surplus sludge is regularly pumped and transported out (two to three times a year). Design features: the tank is designed as A3 steel structure.

(10) fan setting purpose: to supply oxygen, aeration and mixing in a / O biochemical tank and regulating tank. Design features: there are two fans, one for use and one for standby (alternate operation). The fan is designed by pepside (Jiangsu) Co., Ltd., which has the characteristics of small volume, low noise, sufficient air volume, stable and reliable performance.

(11) the host computer of PC automatic control cabinet is imported from Japan, and other components are electrical components of Siemens company for full-automatic program control operation.


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